The present work had the objective to evaluate the effects of supplementation with selenium intraruminal pellets in grazing
heifers, which were selected from a farm, located in the southern region of Chile, with a history of low glutathione peroxidase
(GSH-Px, E.C. 1.11.1.9) activity in the blood and selenium deficiency in the grass.
One hundred and sixty Black Friesian heifers with 7-8 months of pregnancy were selected and asigned in two similar groups,
defined as treated and control group, keeping them on similar management conditions during 15 months of the experiment. The
treated group were supplemented two months before calving with two intraruminal pellets, containing 3 g of elemental selenium
(Permasel®). In ten heifers of each group were determined blood GSH-Px activity according to a kinetic technique NADPH-dependent,
in heparinized blood samples which was obtained every two months, beginning from the administration of pellets. There were
also evaluated reproductive and sanitary parameters, using reproductive, health and dairy control records of the farm. There
were calculated the average and standard deviation for each group and the differences between groups and periods using ANOVA,
"t" Student or χ2 with 95% of confidence (P<0,05).
In the beginning of the experiment the blood GSH-Px activities of the two groups were similar (P>0,05). However, the enzyme
activity increased in the treated group (P<0,05) from the second month of sampling (P<0,05), observing greater values at the
end of the study. The treated group also showed differences in fertility variables, having shorter intervals from parturition
to first service and from parturition to conception (P<0,05). Nevertheless, there were no differences between groups (P>0,05)
in the first service pregnancy rate and in the total pregnancy index. Similarly, there were no observed differences (P>0,05)
between groups in number of cases of abortion, neonatal death and endometritis. The number of somatic cells in milk was similar
in the two groups (P>0,05) during the first two months of lactation, but in the third month there was an increase in the proportion
of animals with less than 100,000 cells/ml in the treated group, while this proportion decreased (P>0,05) in the control animals.
Also, the control group had a higher linear score of somatic cells in the third month of lactation (P<0,05).
According to these results, it was conclude that, on the conditions of this experiment, the supplementation with two intraruminal
pellets of 3 g of elemental selenium in heifers before calving, caused an increment in the blood glutathione peroxidase activity
to adequate levels during one year at least, leading to an improvement in fertility and health condition of the cattle.